The present invention relates to a tilt detecting device using a liquid member to form a free liquid surface.
The present applicant proposed a tilt detecting device using a free liquid surface and a survey instrument comprising the tilt detecting device in JP-A-11-118482(U.S. Pat. No. 6,204,498).
Referring to FIG. 11 and FIG. 12, description will be given on general features of the tilt detecting device as described in JP-A-11-118482.
A first light source 1, e.g. an LED, for emitting a light beam in a horizontal direction is provided. On an optical axis of the first light source 1, a first condenser lens 2, a first pattern 3, a second condenser lens 4, and a first half-mirror 5 are arranged. On an optical axis of a reflection light from the first half-mirror 5, a liquid member 6 is disposed, and the liquid member 6 is accommodated in a container 7 so that a free liquid surface 6a is formed. As a material of the liquid member 6, a liquid having adequate viscosity, e.g. silicone oil, is used. The first light source 1 and the free liquid surface 6a of the liquid member 6 are arranged at conjugate positions.
The light beam reflected by the first half-mirror 5 is reflected by the free liquid surface 6a and passes through the first half-mirror 5. On an optical axis of the transmission light from the first half-mirror 5, a third condenser lens 9 and a photodetection means 11 are arranged.
The light beam emitted from the first light source 1 is turned to a parallel beam by the first condenser lens 2. The light beam passing through the first pattern 3 passes through the condenser lens 4 and is reflected upward by the first half-mirror 5 and is reflected by the free liquid surface 6a. Then, after passing through the first half-mirror 5 and the third condenser lens 9, the beam is received by the photodetection means 11. The second condenser lens 4 and the third condenser lens 9 form an image of the first pattern 3 on the photodetection means 11. The result of the photodetection of the photodetection means 11 is inputted to an arithmetic processing unit 13.
A reference position is set on the photodetection means 11. When the tilt detecting device itself is at a horizontal position, a pattern image reflected from the free liquid surface 6a and formed on the photodetection means 11 is aligned with the reference position.
When the tilt detecting device is tilted at an angle of xcex8, the free liquid surface 6a is relatively tilted with respect to the device at an angle of xcex8 because the free liquid surface 6a is maintained in a horizontal direction. Therefore, if it is supposed that a refractive index of the liquid member 6 is n, the light beam reflected by the free liquid surface 6a is deflected at an angle of 2nxcex8 with respect to the incident light optical axis. If it is supposed that a focal length of the third condenser lens 9 is f, an amount of movement L on the photodetection means 11 is given by the following equation (1).
L=fxc3x97tan(2nxcex8)xe2x80x83xe2x80x83(1)
By the arithmetic processing unit 13, the value L of the pattern image with respect to the reference position can be calculated, and tilting xcex8 of the tilt detecting device itself can be further obtained by inverse calculation.
In the conventional type tilt detecting device as described above, the reference position is set on the photodetection element, and there is possibility that the reference position is changed over time with respect to a main unit of the surveying instrument which comprises the tilt detecting device. Also, the photodetection element may be moved due to the change of environmental temperature. In such case, there has been a problem that the reference position is displaced, and error may occur in the tilt detection.
Also, in a system provided with the tilt detecting device, e.g. in a surveying instrument, etc., a unit having a function suitable for the work is removably mounted in some cases. In these cases, only tilting of an assembly where the tilt detecting device is mounted can be detected by the conventional type tilt detecting device, and tilting of the unit remains indefinite.
It is an object of the present invention to provide a tilt detecting device, by which it is possible to accurately detect tilting without being influenced by error over time or by the change in environmental temperature, and further, to detect tilting including other assembly or assemblies even when other assembly or assemblies are mounted on an assembly where the tilt detecting device is provided.
To attain the above object, the tilt detecting device according to the present invention detects tilt by a reflection surface from a free liquid surface and comprises a photodetection element, a liquid member for forming the free liquid surface, a fixed reflection member fixed on a structural member, a free liquid surface light projecting system for projecting a light toward the liquid member, a fixed reflection member light projecting system for projecting a light toward the fixed reflection member, a photodetection optical system for guiding the reflection light from the free liquid surface of the liquid member and a reflection light from the fixed reflection member toward the photodetection element, and an arithmetic processing unit for calculating deviation based on two reflection images received by the photodetection element. Further, the present invention provides the tilt detecting device as described above, wherein a first pattern is provided in the free liquid surface light projecting system, and a second pattern is provided in the fixed reflection member light projecting system, and the reflection images are pattern images. Also, the present invention provides the tilt detecting device as described above, wherein the first pattern and the second pattern are darkfield patterns. Further, the present invention provides the tilt detecting device as described above, wherein the free liquid surface light projecting system and the fixed reflection member light projecting system project linearly polarized light beams of the same phase, wherein a xcex/4 polarization member is provided in a common optical path for incidence and reflection of the light to and from the liquid member, wherein a xcex/4 polarization member is provided in a common optical path for incidence and reflection of the light to and from the fixed reflection member, and wherein the photodetection optical system comprises a polarization optical member, which allows only the reflection light from the liquid member and the fixed reflection member to pass. Also, the present invention provides the tilt detecting device as described above, wherein a direction of polarization of the projected light beam is determined by a polarizing plate. Further, the present invention provides the tilt detecting device as described above, wherein each of the free liquid surface light projecting system, the fixed reflection member light projecting system, and the photodetection optical system comprises a beam splitter, and the beam splitter has a surface tilted with respect to a transmission light passing through a semi-transmitting surface. Also, the present invention provides the tilt detecting device as described above, wherein the free liquid surface light projecting system and the fixed reflection member light projecting system comprise a common light source, and a beam splitter for splitting the light beam from the light source to a light beam directed to the liquid member and a light beam directed to the fixed reflection member. Further, the present invention provides the tilt detecting device as described above, wherein there is provided a pattern arranged in such manner that the light beam from the common light source can pass through, and the pattern further comprises a pattern where the light beam directed to the liquid member can pass through and a pattern where the light beam directed to the fixed reflection member can pass through. Also, the present invention provides the tilt detecting device as described above, wherein the liquid member is accommodated in a container, and an upper surface of the container is tilted with respect to the transmission light passing through the free liquid surface. Further, the present invention provides the tilt detecting device as described above, wherein the free liquid surface light projecting system comprises a half-mirror for reflecting the light beam toward the liquid member and for allowing the reflection light from the liquid member to pass, and the half-mirror and the liquid member are optically integrated with each other. Also, the present invention provides the tilt detecting device as described above, wherein the half-mirror and the liquid member are optically integrated with each other via an optical member. Further, the present invention provides the tilt detecting device as described above, wherein a refractive index of the liquid member is approximately equal to a refractive index of the optical member. Also, the present invention provides the tilt detecting device as described above, wherein an anti-reflection membrane is provided between the liquid member and the optical member.